This invention relates to centrifugal pumps in which fluid is led to the "eye" or center of an impeller through an inlet, and the pressure is produced as the fluid is rotated by the impeller at high speed. Higher fluid pressure can be obtained when the high speed fluid is slowed to a lesser velocity.
The total pressure of a particle of fluid is made up of its static pressure, which is what is measured on a pressure gauge, and its dynamic pressure, which depends on the speed at which it is moving. The dynamic pressure is the pressure exerted on an object suddenly introduced in front of the moving particle. The dynamic pressure increases as the square of the velocity. It is not possible to convert all the dynamic pressure in a flowing fluid to static pressure, but it is possible to recover about 50 to 80 percent of the dynamic pressure. One method of recovering some of the dynamic pressure is to slowly increase the delivery channel area, as for example with a diverging taper of about 8.degree.. This recovery can be accomplished in a diffuser, i.e., fluid passages which carry fluid from an impeller to the inlet of another impeller or to a pump discharge. Most pumps of any size have some type of diffuser. In many of the so-called centrifugal pumps, there are a plurality of pump stages, i.e., a plurality of impellers, each discharging into a diffuser, and to a final discharge.
The usual vertical diffuser pump assembly comprises a plurality of interconnected castings, for example, an intake casting, one or more bowl castings, and a discharge head. A centrifugal impeller is associated with each bowl casting and each impeller is driven by a common shaft connected to an electric motor or other prime mover. The bowl casting includes an acorn, i.e., the inner structural core of the pump in the form of a conical-shaped part which defines the inner profile of the diffuser passageways and which surrounds the shaft and retains a shaft sleeve bearing. An annular wall of the acorn defines a portion of an impeller chamber with another portion of the impeller chamber being defined by the next preceeding casting, whether it be a bowl casting or intake casting. In addition to the acorn portion, the bowl casting comprises an outer, generally circular by cylindrical wall joined to the conical wall of the acorn by a plurality of connecting and generally radially oriented walls or vanes, thus forming a plurality of fluid passageways for the flow of fluid from the impeller. The radially oriented walls or vanes terminate short of the ends of the bowl castings to thus define generally annular chambers for receiving and discharging fluid to and from the passageways, respectively. In the usual pump described, each of the fluid passageways has a cross-sectional area which increases from inlet to outlet, i.e., in the direction of the fluid flow.